Filtering sam/bam by using CIGAR deletion sites
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2.5 years ago
ag1194 • 0

Hi,

I have a CLIP-Seq data and after mapping, I want to filter my sam files for reads containing deletion by using CIGAR & MAPQ >10. Is there a way in samtools to subset my sam file containing reads MAPQ>10 & with deletion?

Thank you very much!

alignment next-gen • 2.1k views
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Thank you very much!!! I'll try and see samjdk first and also pysam to see the results.

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2.5 years ago
Geparada ★ 1.4k

I would do something like:

samtools view file.bam | awk '($6 ~ /D/) && ($5>10)'

($6 ~ /D/) means "deletion in CIGAR" and $5>10 means MAPQ>10

I really like awk oneliners for doing quick filters like this.

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With samtools view & awk tools, I cannot keep the header in my output bam. Is there a way to have filtered bam with header with awk tool? Thanks!!!

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samtools view -h file.bam | awk '($0 ~ /^@/) || (($6 ~ /D/) && ($5>10))'
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Hey when I try to pipe this to a new bam like so

samtools view -h file.bam | awk '($0 ~ /^@/) || (($6 ~ /D/) && ($5>10))' > new.bam

I can't view the new.bam. Any ideas?

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The result will be sam, not bam. To save it as sam, you need to pipe it to samtools view -b

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2.5 years ago

using samjdk: http://lindenb.github.io/jvarkit/SamJdk.html

java -jar dist/samjdk.jar -e 'return !record.getReadUnmappedFlag() && record.getMappingQuality()>10 && record.getCigar().getCigarElements().stream().map(C->C.getOperator()).anyMatch(O->O.equals(CigarOperator.D) || O.equals(CigarOperator.N)); ' input.bam
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2.5 years ago
Vitis ★ 2.4k

Pysam is a good tool to manipulate SAM/BAM with various attributes like CIGAR and mapping quality.

https://pysam.readthedocs.io/en/latest/

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import pysam
inbam = pysam.AlignmentFile("my_bamfile.bam")
outbam = pysam.AlignmentFile("filtered_bamfile.bam", template=inbam)
for read in inbam.fetch(until_eof=True):
    if read.mapping_quality > 30 and 'D' in read.cigarstring:
        outbam.write(read)
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